Yanlu Li

Performance tradeoff between lateral and interdigitated doping patterns for high speed carrier-depletion based silicon modulators

Carrier-depletion based silicon modulators with lateral and interdigitated PN junctions are compared systematically on the same fabrication platform. The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance. The low VπLπ of the interdigitated PN junction is employed to demonstrate 10 Gbit/s modulation with 7.5 dB extinction ration from a 500 µm long device whose static insertion loss is 2.8 dB. In addition, up to 40 Gbit/s modulation is demonstrated for a 3 mm long device comprising a lateral diode and a co-designed traveling wave electrode.

Reflectionless grating couplers for Silicon-on-Insulator photonic integrated circuits

We propose a novel grating coupler design which is inherently reflectionless by focusing the reflected light away from the entrance waveguide. The design rules for this reflectionless grating coupler are explained and the grating coupler design is investigated by means of 3D FDTD simulations for the case of a Silicon-on-Insulator based platform.

Compact grating couplers on silicon-on-insulator with reduced backreflection

The backreflection in commonly used grating couplers on silicon-on-insulator (SOI) is not negligible for many applications. This reflection is dramatically reduced in our improved compact grating coupler design, which directs the reflection away from the input waveguide. Realized devices on SOI show that the reflection can be reduced down to -50 dB without an apparent transmission penalty.

Reflectionless Tilted Grating Couplers With Improved Coupling Efficiency Based on a Silicon Overlay

Grating couplers are important photonic devices on a complementary metal-oxide-semiconductor compatible silicon-on-insulator platform to couple light between optical waveguides and free space optical components or fibers. In this letter, we report the combination of a tilted grating coupler design, which strongly suppresses the back-reflection for light incident on the grating coupler from a waveguide, and a silicon overlay locally deposited on top of the grating region, which enhances the coupling efficiency of the grating coupler, by means of simulation and experiment. The fabricated tilted focusing grating couplers with silicon overlay show a coupling efficiency of -2.2 dB in combination with a back-reflection of around -40 dB when excited from the silicon waveguide. The tilted design also provides an alternative approach to enhance the transmission of a grating coupler when the thickness of the Si overlay is not optimized.

On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement

Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement.

Heterodyne laser Doppler vibrometers integrated on silicon-on-insulator based on serrodyne thermo-optic frequency shifters

Miniaturized laser Doppler vibrometers (LDVs) have many advantages over conventional bulk LDVs. In this paper, the realization of a miniaturized heterodyne LDV integrated on silicon-on-insulator substrate is reported. The optical frequency shifters in these on-chip LDVs employ a serrodyne technique, and they generate a frequency shift at 2 kHz. Vibrations of a mirror for the frequency range between 1.1 and 123 Hz and the velocity range between 0.8 and 400 μm/s are measured by both an on-chip LDV and a commercial LDV. The measurement results agree well. A compensation method for the influence of on-chip spurious reflections is also demonstrated.

Expanding the Silicon Photonics Portfolio With Silicon Nitride Photonic Integrated Circuits

The high index contrast silicon-on-insulator platform is the dominant CMOS compatible platform for photonic integration. The successful use of silicon photonic chips in optical communication applications has now paved the way for new areas where photonic chips can be applied. It is already emerging as a competing technology for sensing and spectroscopic applications. This increasing range of applications for silicon photonics instigates an interest in exploring new materials, as silicon-on-insulator has some drawbacks for these emerging applications, e.g., silicon is not transparent in the visible wavelength range. Silicon nitride is an alternate material platform. It has moderately high index contrast, and like silicon-on-insulator, it uses CMOS processes to manufacture photonic integrated circuits. In this paper, the advantages and challenges associated with these two material platforms are discussed. The case of dispersive spectrometers, which are widely used in various silicon photonic applications, is presented for these two material platforms.

Realization of fiber-based laser Doppler vibrometer with serrodyne frequency shifting

We demonstrate a laser Doppler vibrometer (LDV) based on the serrodyne frequency shifting technique. A proof-of-principle system is implemented on the basis of fiber-optic components but opens the way toward an ultracompact integrated LDV system on a silicon chip. With a low laser power of 50  μW, the serrodyne LDV was able to measure submicrometer vibrations with frequencies in the audio range.

Integrated design for integrated photonics: from the physical to the circuit level and back

Silicon photonics is maturing rapidly on a technology basis, but design challenges are still prevalent. We discuss these challenges and explain how design of photonic integrated circuits needs to be handled on both the circuit as on the physical level. We also present a number of tools based on the IPKISS design framework.

A polymer-based surface grating coupler with an embedded Si3N4 layer

Polymer has been considered to be an ideal material option for integrated photonics devices. To measure these devices, normally the route of edge coupling is chosen to couple the light into or out of the polymer waveguide, which, however, demands a more difficult alignment procedure compared to the surface coupling. Due to the relatively low refractive indices of polymers, implementing the surface grating coupler for surface coupling in this material system remains a challenge. In this paper, we present a polymer-based surface grating coupler. Rather than through expensive complementary metal–oxide–semiconductor (CMOS) fabrication, the device is fabricated through a simple and fast UV-based soft imprint technique utilizing self-developed low-loss polymer material. The coupling efficiency is enhanced by embedding a thin Si3N4 layer between the waveguide core and under cladding layer. Around −19.8 dB insertion loss from single-mode fiber (SMF) to single-mode fiber is obtained for a straight waveguide with a...